Heat exchanger structure for steam generators

ABSTRACT

Heat exchanger structure for steam generators to be used with nuclear installations, chemical installations, such as petrochemical plants and the like. The steam generator has primary and secondary pressure barriers between which connecting pipes extend, and within the latter pipes are heat-exchanging tubes which extend from tube sheets which are situated within the connecting pipes. At least part of these tube sheets form parts of the primary and secondary pressure barriers.

United States Patent Lippitsch I [451 Apr. 18, 1972 HEAT EXCHANGERSTRUCTURE FOR Ref r nc s Cited STEAM GENERATORS UNITED STATES PATENTS[72] inventor: .losei Llppltsch, Graz, Austria 2,222,349 11/1940Jones.... ..l22/249 X [73] Assignee: wnanebmm AG, Vienna Austria3,256,932 6/1966 Schlrchtmg ..l22/249 X 22 p M 25 959 PrimaryExaminer-Edward J.-Michael 1 le Ju Attorney-Steinberg8z Blake [2]] Appl.No.: 836,296

[57] ABSTRACT [30] Foreign Application Priority D t Heat exchangerstructure for steam generators to be used with nuclear installations,chemical installations, such as June 26, Austria ..A petrochemicalplants and [he like The steam generator ha primary and secondarypressure barriers between which con- [52] U.S.Cl ..165/81 1 nectingpipes extend, and within the latter pipes are heat- [51] lm. Cl ..F28f7/00 ng g t s h h xt nd from tube sheets which are 58 Field of Search..165/8l;122/249,250 Situated within the connecting P P At least p ofthese tube sheets form parts of the primary and secondary pressurebarriers.

HEAT EXCHANGER STRUCTURE FOR STEAM GENERATORS BACKGROUND OF THEINVENTION The present invention relates to steam generators.

In particular, the present invention relates to steam generators whichare capable of being used in plants where the heat is derived from anuclear reactor, or in chemical installations where the heat is derivedfrom chemical equipment, such as in the case of the petrochemicalindustry.

In installations of the above type the heat for the steam generator isderived from hot gases which are directed into the heat exchanger sothat the feedwater which is fed into the boiler tubes will be vaporizedto form steam which can then be superheated.

With installations of this type a problem is encountered when failuresoccur. Thus, when failure occurs the space in which the steam generatoris located can become rapidly filled with hot gas creating extremelydangerous situations which may be highly injurious to personnel andequipment. Moreover, even if it is possible under such circumstances tocut off the source of the hot gases so that access may be had to thefaulty steam generator, it is not always possible to efiiciently andinexpensively work on the steam generator so that the source of thefaulty operation thereof can be corrected. For example, it may be thatone or more tubes of the heat exchanger unexpectedly start to leak.Under such conditions it is not always possible to place such leakytubes in a condition where they no longer participate in the operationof the heat exchanger, so that under these circumstances even if arelatively small number of tubes are the source of trouble, it may benecessary to shut down an entire installation until proper repairs canbe effected.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide a construction which will avoid the abovedrawbacks.

In particular, it is an object of the invention to provide aconstruction which will afford an opportunity to shut ofi the supply ofhot gases, in the event that faulty operation of a steam generator, ininstallations of the above type, is encountered.

Also, it is an object of the invention to provide a construction whichwill make it possible to prevent faulty tubes from participating in theoperation of the heat exchanger without necessarily requiringdismantling of the entire heat exchanger structure.

In particular, it is an object of the invention to provide aconstruction which makes it easily possible to plug up thoseparticular'tubes which are the source of a faulty operation, withoutremoving such tubes from the installation, so that it is possible veryquickly and inexpensively to resume operations with the steam generator.

Furthermore, it is an object of the invention to provide a constructionwhere the parts are capable of expanding and contracting in response totemperature changes without providing undesirably great stresses on thestructure.

According to the invention the steam generator has a heatexchangingstructure which includes primary and secondary barriers spaced from eachother. Connecting pipes extend at least in part between the primary andsecondary barriers, and heat-exchanging tubes are situated within theseconnecting pipes and extend from tube sheets which are also situatedwithin the connecting pipes. These tube sheets themselves form, at leastpartly, parts of the primary and secondary pressure barriers.

BRIEF DESCRIPTION OF DRAWING The invention is schematically andfragrnentarily illustrated by way of example in the longitudinalsectional elevation of a heat exchanger which forms part of a steamgenerator.

- 2 DESCRIPTION OF A PREFERRED EMBODIMENT The heat-exchanger structurewhich is shown in elevation in the drawing is designed for use withnuclear installations. However, the invention is not limited to such useand can be used with chemical installations, in particular in thepetrochemical industry. The heat-exchanger illustrated forms a steamgenerator. It includes a primary pressure barrier 1 and a secondarybarrier 2. The heat-exchanger tubes in which the actual heat exchangetakes place are in the form of bundles of tubes, 6, 7, and 8. Thesebundles of tubes are schematically illustrated. The bundle of tubes 6serves to preheat the liquid and also, according to the particularoperation, to vaporize the liquid, while the bundle of tubes 7 whichreceives the fluid from the tubes 6 serves to superheat the steam whichis generated. The bundle of tubes 8 serves as an intermediatesuperheater, but the presence of several bundles of tubes is notessential to the invention.

The heat is derived from a gaseous medium which flows into or out of theheat exchanger through the conduit 9. This conduit 9 serves in theillustrated example to provide communication between the heat exchangerand an unillustrated reactor. This gaseous medium fills the entire innerspace of the heat exchanger. It flows through leakage places of thesecondary barrier 2, such leakage places being formed by cracks,clearances, and the like at the secondary pressure barrier 2. As isindicated in the drawing, the bundles of tubes 7 and 8 extend from tubesheets 3 which are connected by plugs 5, which respectively extend fromthese plates 3, with relatively short connecting pipes extending fromand through the barrier 2 and forming part of the latter with these tubesheets 3 also forming part of the secondary pressure barrier 2. Thus,due to the possibility of leakage of the hot gas through the secondarypressure barrier 2, it is possible for this hot gas to flow into thechamber between the primary and secondary pressure barriers.

An important safety purpose is served by the division of the structureintoprimary and secondary pressure barriers. Thus,

in the event of failure of the primary pressure barrier l, in particularat the cover of the heat exchanger, there will not be an immediateescape of the gaseous medium into the space 10 around the heatexchanger. In the event that there is a failure of the primary pressurebarrier, the secondary pressure barrier 2 takes over the functions ofthe primary pressure barrier at least for a length of time sufficient toseparate the source of the hot gas from the heat exchanger or toterminate the operation of .the reactor.

The tube sheets 3 are situated withinconnecting pipes 4 which areconnected in a gas-tight manner with and extend through the primarypressure barrier 1. Those pipes 4 which serve to convey a hot mediumwhich flows therethrough are provided with heat insulation 15. Theseconnecting pipes 4 are provided at their connections with the tubesheets with an enlarged diameter so that it is possible to situateplugging machines in the pipes 4 in order to close ofl damaged tubeswhich are connected to the tube sheets 3. In this way it becomespossible for the faulty tube or tubular coil to be placed in a conditionwhere the cooling medium no longer flows through such tubes. The severalbundles of tubes 6-8 are, for example, welded into openings which areformed n the tube sheets 3. Thus, just above these tube sheets 3 for thebundles of tubes 7 and 8 the connecting pipes 4 form collecting chambersin which the medium which flows in the interior of the tubes collects,and these collecting chambers formed by the connecting pipes 4 serve todirect the fluid through the primary pressure barrier 1. Outside of andbeyond the primary pressure barrier l the connecting conduits 11 and 12communicate with the connecting pipes 4, these conduits extendingperpendicularly with respect to the pipes 4. Thus, the conduit 11 servesas a supply conduit for a liquid such as water which will be convertedinto steam while the conduits 12 are discharge conduits through whichthe steam flows to any consumer units which utilize the steam. The topends of the pipes 4 are covered by closure plates 13 and 14, so that itis a simple matter upon removal of such closure plates to have easyaccess to the connecting pipes 4. As a result of this easy access to theconnecting pipes 4 it is possible to easily introduce the pluggingmachine into a connecting pipe 4 in order to plug up a damaged ordefecting tube. In this way such tubes can be closed so that they willno longer participate in the operation of the heat exchanger.

The central or innermost collecting chamber of the heat exchanger has aconstruction which is somewhat difierent from the other chambers formedby the connecting pipes 4. Thus, it is this central or innermostconnecting pipe 4' in which the bundle of tubes 6 is accomodated. Inthis case the tube sheet 3' into which the heat-exchanger tubes arerolled forms a special part of the primary pressure barrier 1. Thus, itis apparent from the drawing that the uppermost tube sheet 3'illustrated therein is the only one of the tube sheets which is situatedat and forms part of the pressure barrier 1. Within this central orinnermost connecting pipe 4' there is beneath the tube sheet 3 therein asecond plate which is similar to a tube sheet, this plate 18 formingpart of the secondary pressure barrier 2, while the remaining tubesheets 3 situated at the lower elevation illustrated in the drawing alsoform parts of the secondary barrier 2. This plate 18 is formed with aplurality of bores passing therethrough so that the bundle of heatexchanging tubes 6 can extend through these bores. In this case also theplate 18 is formed with clearances, which may take the form of cracks,gaps, or the like, so that upon failure of the primary pressure barrierthe hot gaseous medium can only escape slowly. With this constructionthere is moreover an outer cylinder 16 which surrounds theheat-exchanger structure which extends between the primary and secondarypressure barriers. This cylinder 16 is fixedly connected with thesecondary pressure barrier 2. However, it has a pin-andslot connection17 with the primary pressure barrier 1. It is therefore possible for thecylinder 16 and the primary pressure barrier l to move axially one withrespect to the other in response to expansion and contraction due totemperature changes.

Those connecting pipes 4 which form collecting chambers for hot fluidmedium are provided at the locations where they pass through thepressure barrier 1 with surrounding sleeves 19 which form heat traps, sothat heat is conducted away only to a small extent in the primarypressure barrier 1.

The plug-type of connection formed by the plugs which respectivelyextend from the lower tube sheets 3 where the latter are connected withthe short connecting pipes of the secondary barrier 2, have a slidableengagement with the interior of these short connecting pipes, so that itis possible to provide for free expansion and contraction of the pipeconnections 4, which serve as the collecting chambers, with respect tothe pressure barrier 2, as a result of the possibility of free axialshifting between the lower tube sheets 3 and the secondary barrier 2 atthe plugs 5 which are freely slidable with respect to the relativelyshort connecting pipes of the pressure barrier 2. In this wayundesirable additional stressing of the secondary pressure barrier 2, asa result of heat stresses, is avoided. In the same way, this latterfeature results in lesser stressing of the primary pressure barrier l asa result of nonuniform heat stresses.

For the means 5 which provides the slidable or shiftable connectionbetween the lower tube sheets 3 and the short connecting pipes of thesecondary pressure barrier 2, it is preferred to use around thepiston-shaped plugs piston sealing rings which provide the slidableconnection.

At the innermost pipe connection 4' there will in general be coldfeedwater which is fed to the heat exchanger which forms the steamboiler. This feedwater is vaporized into steam without being removedfrom the surrounding pressure vessel. The pipe connections 4, inparticular those through which the hot fluid flows out of the heatexchanger and in which the hot fluid is collected, or in other wordsthose pipe connections 4 in which steam is conveyed, are provided withheat-insulating surrounding casings 15 in order to avoid heat lossesbetween the primary and secondary pressure barriers.

What is claimed is:

1. In a steam generator, primary and secondary pressure barriers, aplurality of connecting pipes extending at least in part between saidbarriers, and plurality of tubes and tube sheets within said pipes, saidtube sheets being situated between said primary and secondary pressurebarriers and at least part of said tube sheets forming parts of saidprimary and secondary pressure barriers.

2. The combination of claim 1 and wherein said secondary barrier formsan inner cover of a heat-exchanger pressure vessel, a plurality of pipeconnections respectively connecting at least some of said tube sheetswith said inner cover, and means providing between said tube sheets andpipe connections a shiftable joint so that the latter pipe connectionsand tube sheets are capable of shifting one with respect to the other.

3. The combination of claim I and wherein said pies connect said tubesheets with said primary pressure barrier in a gas-tight manner.

4. The combination of claim 3 and wherein said pipes extend through saidprimary barrier, said pipes respectively having in the region of saidtube sheets diameters larger than the diameters of said pipes where theypass through said primary pressure barrier.

5. The combination of claim 3 and wherein said pipes are straight at theregions thereof which extend between primary and secondary pressurebarriers.

6. The combination of claim 1 and wherein an outer cylinder surroundsand interconnects said primary and secondary barriers, and pin-and-slotmeans interconnecting said outer cylinder with said primary barrier.

7. The combination of claim 3 and wherein an insulating means coactswith said pipes between said primary and secondary barriers forinsulating the latter against heat losses.

8. The combination of claim 1 and wherein said tubes include aninnermost bundle of tubes and an innermost tube sheet from which saidinnermost bundle of tubes extend, said innermost tube sheet being theonly one of said sheets which form part of said primary pressurebarrier, and a second tube sheet through which said innermost bundle oftubes extend with clearance, said second tube sheet forming a part ofsaid secondary pressure barrier.

1. In a steam generator, primary and secondary pressure barriers, aplurality of connecting pipes extending at least in part between saidbarriers, and plurality of tubes and tube sheets within said pipes, saidtube sheets being situated between said primary and secondary pressurebarriers and at least part of said tube sheets forming parts of saidprimary and secondary pressure barriers.
 2. The combination of claim 1and wherein said secondary barrier forms an inner cover of aheat-exchanger pressure vessel, a plurality of pipe connectionsrespectively connecting at least some of said tube sheets with saidinner cover, and means providing between said tube sheets and pipeconnections a shiftable joint so that the latter pipe connections andtube sheets are capable of shifting one with respect to the other. 3.The combination of claim 1 and wherein said pipes connect said tubesheets with said primary pressure barrier in a gas-tight manner.
 4. Thecombination of claim 3 and wherein said pipes extend through saidprimary barrier, said pipes respectively having in the region of saidtube sheets diameters larger than the diameters of said pipes where theypass through said primary pressure barrier.
 5. The combination of claim3 and wherein said pipes are straight at the regions thereof whichextend between primary and secondary pressure barriers.
 6. Thecombination of claim 1 and wherein an outer cylinder surrounds andinterconnects said primary and secondary barriers, and pin-and-slotmeans interconnecting said outer cylinder with said primary barrier. 7.The combination of claim 3 and wherein an insulating means coacts withsaid pipes between said primary and secondary barriers for insulatingthe latter against heat losses.
 8. The combination of claim 1 andwherein said tubes include an innermost bundle of tubes and an innermosttube sheet from which said innermost bundle of tubes extend, saidinnermost tube sheet being the only one of said sheets which form partof said primary pressure barrier, and a second tube sheet through whichsaid innermost bundle of tubes extend with clearance, said second tubesheet forming a part of said secondary pressure barrier.